Gec entered the University of Ljubljana, where she studied archaeology under Srečko Brodar, Josip Korošec [sl] and Josipa Klemenca,[2] graduating in 1956,[1] and by 1957, was publishing in the name of Plesničar.

[2][1] She led numerous excavations at the site, discovering an Early Christian religious center and baptistery, necropolises, the northern gate of the city, several residential areas and a Roman Forum.

[2] Unlike her predecessor, Jože Plečnik, who redesigned the Roman walls to create a pleasing artificial display of the artifacts, Plesničar adopted a minimal intervention approach, leaving remains in situ.

[7] In 1967, Jakopič Gardens, now known as Emonan House, were opened to the public, after Plesničar's excavations[9] in the 1963–1964 season uncovered the dwelling remains of a wealthy family on the outskirts of Ljubljana in the Mirje neighborhood.

She prepared, with the assistance of colleagues numerous exhibitions, such as the 1973 Frescoes of Emonia and the Archaeological Heritage of Ljubljana of 1996 and created international networks cooperating with museums in Aquileia, Belgrade, Krakow, Pula and Warsaw, among other cities.